1. Field of the Invention.
The present invention relates to a projection cathode ray tube for enlarging and projecting a small image which is formed on the cathode ray tube by using a projection lens and a single cathode ray tube as an image source, and more particularly, related to a projection television receiver for forming each red, green and blue image on one cathode ray tube, projecting the formed images using one lens and embodying a screen larger than that of a 40 inch television set as an image display device for a projection television receiver having high definition.
2. Background of the Related Art
Recently, in projection television receivers embodying a large sized screen, the image forming ability of the lens for enlarging and projecting an image which is formed on each red, green and blue fluorescent surface of the cathode ray tube, has been developed and the requirements for a projection lens as an essential element are important.
In such an environment, the lenses have improved image forming capabilities and ability.
In lens design, the differentiation of the lens related to a configuration method, number and shape of the lens even though in the same lens design concept is attempted through different lens design and development. For example, U.S. Pat. Nos. 4,948,237 and 4,697,892 are examples of such differentiation of the lens.
The general projection lens which is listed in the above-mentioned technology has a good image forming ability in the respective wavelength field by executing aberration correction at a predetermined wavelength.
In example, the predetermined wavelength is an e-line (546.1 mm) which is next to a central wavelength of the green cathode ray tube.
However, the chromatic aberration is caused because the lens which is designed for using in the e-line is used at the red and the blue cathode ray tubes in the same condition as when the light is deviated from the e-line and the spectral spectrum of the green cathode ray tube does not have a homogeneous property and emits light of the red color and the blue color zones.
Thus, in the optical system of where chromatic aberration is not corrected, in other words, where aberration is not corrected simultaneously in the zones of the red, the green and the blue color wavelengths, the system, and is not suitable for a display lens for a high definition and a high image because the optical system causes deterioration of definition and image in the television receiver set.
The conventional, three cathode ray tubes such as a red, a green and a blue cathode ray tubes and displaying device which displays images onto the screen by enlarging and projecting each image from the cathode ray tubes will be described in FIG. 1.
The device shown in FIG. 1 will be described as an example of a conventional projection cathode ray tube. 5 The above-mentioned cathode ray tube consists of a first through a third cathode ray tubes 101 through 103 for respectively emitting a red, a green and a blue colored image which are formed on a fluorescent surface and a first through a third lens assemblies 104 through 106 for a red, a green and a blue image formed on the side of the first through the third cathode ray tubes 101 through 103, enlarges and projects the red, the green and the blue images for displaying the images onto a screen 100.
A conventional cathode ray tube which is formed as an aforementioned manner will be described in detail with reference to FIG. 1.
First, each forming image of the red, the green and the blue color is emitted from the fluorescent surface of the first through the third cathode ray tubes 101 through 103 having a red, a green and a blue colors for embodying colors and received at the first through the third lens assemblies 104 through 106.
The first through the third lens assemblies 104 through 106 enlarge and project the received red, green and blue images for forming images and displays the images onto the screen 100.
In other words, when each red, green and blue colored image which is respectively formed on the fluorescent surface of the first, the second and the third cathode ray tubes 101 through 103, is emitted and received to the first through the third lens assemblies 104 through 106 for projecting the images, the first lens assembly 104 enlarges and projects the red colored image for forming an image from the first cathode ray tube 101, the second lens assembly 105 enlarges and projects the green colored image for forming an image from the second cathode ray tube 102 and the third lens assembly 106 enlarges and projects the blue colored image for forming an image from the third cathode ray tube 103 and each image is displayed onto the screen 100, accordingly, the red, the green and the blue images for forming an images corresponding to the image source are enlarged and displayed onto the screen 100.
But, as mentioned above, the conventional projection cathode ray tube requires three cathode ray tubes for emitting the red, the green and the blue images for forming images and three lens assemblies for enlarging and projecting the red, the green and the blue images for forming images emitted from the cathode ray tubes and displaying the images onto the screen.
Accordingly, the projection television receiver for embodying a large sized screen by enlarging and projecting formed images on each red, green and blue fluorescent surface of the cathode ray tube essentially requires three lens assemblies in the conventional projection television receiver.
By using three cathode ray tubes and three lens assemblies corresponding to each red, green and blue color for embodying a large sized screen, the productivity is decreased, the operation for adjusting exact focus correction of the three lenses onto the screen is difficult and the size of the projection television receiver is larger. Accordingly, it is unsuitable for using in high definition and high quality video cassette projector optics.
Moreover, when each red, green and blue cathode ray tube and each lens assembly is respectively integrated as one cathode ray tube and one lens assembly, it is difficult to form a structure for, and also effectively gathering the formed images for red, green and blue colors and precisely enlarging and projecting them onto the screen.
Accordingly, it is preferable to develop the projection television receiver having a larger screen compared to a conventional screen size and high resolution without complexity of structure and larger set size due to the structure of the projection cathode ray tube.